A flow cytometer for use in medical and biological fields includes a fluorescence detection device that receives fluorescence emitted by a fluorochrome of a measurement object irradiated with laser light and identifies the kind of the measurement object.
More specifically, in the flow cytometer, a suspension liquid containing a measurement object such as a biological material (e.g., cells, DNA, RNA, enzymes, or proteins) labeled with a fluorescent reagent is allowed to flow through a tube together with a sheath liquid flowing under pressure at a speed of about 10 m/sec or less to form a laminar sheath flow. The flow cytometer receives fluorescence emitted by a fluorochrome attached to the measurement object by irradiating the measurement object in the laminar sheath flow with laser light and identifies the measurement object by using the fluorescence as a label.
The flow cytometer can measure, for example, the relative amounts of DNA, RNA, enzymes, proteins, etc. contained in a cell and can quickly analyze their functions. Further, a cell sorter or the like is used to identify a specific type of cell or chromosome based on fluorescence and selectively and quickly collect only the identified cells or chromosomes alive.
For example, in order to analyze a biological material such as DNA by a flow cytometer, a fluorochrome is previously attached to the biological material by a fluorescent reagent. The biological material is labeled with a fluorochrome different from a fluorochrome attached to a microbead (which will be described later) and is mixed with a liquid containing microbeads having a diameter of 5 to 20 μM and a specific structure such as a carboxyl group provided on the surface thereof. The structure such as a carboxyl group acts on and is coupled to a biological material having a certain known structure. Therefore, simultaneous detection of fluorescence emitted by the microbead and fluorescence emitted by the biological material indicates that the biological material has been coupled to the structure provided on the surface of the microbead. This makes it possible to analyze the characteristics of the biological material. In order to quickly analyze the characteristics of a biological material by using various microbeads having different structures for coupling, very many kinds of fluorochromes are required.
Patent Document 1 describes that a fluorescence relaxation time of fluorescence emitted by irradiating a measurement object such as a microbead with laser light whose intensity is modulated at a predetermined frequency is determined. The fluorescence relaxation time varies depending on the type of fluorochrome used, and therefore the type of the fluorescence can be identified using the fluorescence relaxation tine and the type of the measurement object can be identified by identifying the type of the fluorescence.